The use of a watercraft lift to protect a watercraft from the elements and to ease watercraft user access to a watercraft is well known. Out-of-water storage prevents damage resulting from boat contact with docks, other craft or floating debris. It reduces the possibility of the boat breaking free from its moorage and floating adrift or running aground. Out-of-water storage also lessens boat damage associated with long-term exposure to water and water-based pollutants and the attachment of barnacles or other marine growth to the boat's hull. Once a boat is lifted it can be maintained in its position for extended periods of time, relieving the user of maintenance concerns. A number of lift designs are currently know that provide this basic function. An example of one type of watercraft lift is described in U.S. Pat. No. 5,908,264 to Hey, which is incorporated by reference herein. In its preferred embodiment, a front, a rear and two sides form a rectangular base frame. The frame supports upwardly extending, pivoting booms that are connected to a watercraft platform (typically bunks) upon which the watercraft is positioned. The base frame, booms, and platform combine to form a parallelogram shape when viewed from the side. A hydraulic cylinder connected diagonally across the parallelogram actuates the lift. Extension of the cylinder rotates the booms about their lower end connection to the base frame. Thus, the rotation of the booms moves the watercraft platform (and thus the watercraft on the bunks) between raised and lowered positions. The type of lift described above is often referred to as a four-bar mechanism. U.S. Pat. No. 5,184,914 to Basta and U.S. Pat. No. 5,275,505 to Wilcox demonstrate this type of lift.
Current four-bar lifts, however, suffer from a number of disadvantages in that the current state-of-the art does not include a means and method by which the lifting range of a four-bar lift may be adjusted, which in turn reduces the utility of the device for end-users, manufacturers, and dealers.
For the user, the efficacy and usefulness of the watercraft lift is dependent upon the user's ability to access the watercraft support platform and thereby to enable watercraft ingress and egress to and from the platform. This, in turn, is contingent upon the vertical range of the watercraft platform, which is dictated by the length of the pivoting booms and the maximum angles of movement of those booms relative to horizontal. The use of the watercraft lift will be restricted to situations when the subject water level is within this functional range. If the subject water level drops below this range, the user either will not be able to float his watercraft onto the watercraft support structure, or the watercraft will be stranded on the watercraft support structure. If the subject water level rises above this range, the user will be unable to lift his watercraft above water level and the benefits of the watercraft lift will be lost. Water level variability in different water bodies as well as long-term fluctuation of water levels in specific water bodies caused by such events as seasonal variations in water level, draught or flooding, or governmental water use practices causes a need for a variable range adjustment apparatus for watercraft lifts which will allow the user to adjust the functional range of the watercraft lift for the particular water body in which the watercraft lift will be used.
Boatlift manufacturers currently address the above-stated difficulties by designing, manufacturing and selling four-bar watercraft lifts with booms of the maximum length possible after load constraints are taken into account. There are, however, situations where these large functional ranges create problems and the user would rather adjust the lift to decrease range. A large range may cause the watercraft support structure to be too deep in the water in the fully down position, thereby causing the user to be unable to easily see the watercraft support structure when positioning the boat for lifting and causing an operational time lag. A large range may also cause the watercraft support structure to be too high in the raised position, causing the watercraft to be relatively high in relation to the watercraft entry point, which may be a stationary dock or seawall. This, in turn, may create user access difficulties and safety concerns. Shoreline aesthetics may be also adversely affected by a watercraft that is positioned high above nearby docks—shoreline views of the waterbody and surrounding environment may be blocked by a highly lifted watercraft.
Alternatively, manufacturers may offer lifts with several lifting ranges: Lifts are supplied to dealers with three, four, and five foot booms used to connect the watercraft-supporting bunks to the watercraft base. This creates inventory control difficulties for the manufacturer and dealer in that multiple lifts with the same capacity requirements must be stocked to service the market.
The use of variable range apparatuses in four-bar type lifts is not currently known. The difficulty that has apparently restricted innovation in this area and which is addressed by the current invention is that of excessive loads placed on the booms during operation of the four-bar lift. In the four-bar design, loads placed on the booms increase dramatically as the booms rotate downward and the angles between the boom and the base frame and watercraft platform change from approximately 90 degrees to approximately 180 degrees. Increasing the length of the booms to increase lifting range also cause loads to increase significantly.
A telescoping connection between the watercraft platform and watercraft frame is known to Quastad, U.S. Pat. No. 5,888,019. Quastad describes a ground-based lift with upstanding telescoping posts that are height adjustable. The telescoping post connect the lift's frame to the watercraft support platform and maintain their relative vertical orientation throughout the operation of the lift. The difficulty presented by Quastad's device is that the lifting range of the lift is not actually adjustable. Rather, the vertical position of the base frame relative to the bunks is adjusted, but no increase in the lifting range from the lowered position to the raised position is obtained. The constant vertical position of Quastad's vertical posts cause the difficulty that use of the lift in shallow waters is limited. Because the vertical posts maintain their vertical orientation, the water depth at which Quastad's device may be used is directly and negatively impacted by the user's adjustment of the posts to an elongated position.